PROJECT SUMMARY/ABSTRACT Elevated nighttime blood pressure (BP) is an important risk factor for cardiovascular disease (CVD). Indeed, recent data suggest that elevated nighttime BP may be a stronger risk factor for CVD than elevated daytime BP. African Americans are more likely than other racial/ethnic groups to suffer from elevated nighttime BP, which may partially explain why African Americans are at higher risk of mortality from coronary heart disease and stroke, and have a higher incidence of renal disease, than other racial/ethnic groups in the United States. Thus, investigating methods of reducing nighttime BP in African Americans should be considered an important public health goal. Evidence suggests that melatonin supplementation may help lower nighttime BP. However, randomized studies of melatonin supplementation and nighttime BP in African Americans have not been conducted. The long term goal of this proposal is to examine whether melatonin supplementation helps reduce nighttime BP in African Americans with elevated nighttime BP, and to explore potential mechanisms by which this BP lowering effect might occur. We plan to conduct a pilot randomized, double blind, placebo- controlled, crossover clinical trial (n = 40) examining the effect of melatonin supplementation on nighttime BP in African Americans. The specific aims of the pilot trial are as follows: (i) obtain preliminary data on the efficacy of 4 weeks of nightly melatonin supplementation on nighttime BP in African-American subjects suffering from elevated nighttime BP;(ii) explore sleep factors, sympathetic drive, and vasorelaxation as potential mechanisms by which melatonin may lower nighttime BP;(iii) determine the feasibility of recruiting and randomizing African American subjects with elevated nighttime BP for a melatonin supplementation trial; and (iv) estimate whether melatonin supplementation has any adverse side-effects when taken nightly for four weeks in African-American adults with elevated nighttime BP. Results from the proposed trial should help provide important preliminary data that could be used to guide a larger, more definitive trial.